Image processing method, image processing system, and X-ray computed tomography system

Abstract

Disclosed is image processing: that significantly reduces false images and missing images in reconstructed images, improves reconstruction accuracy; and that can be applied to objects to be observed that are composed of a plurality of components, and to samples having an unknown number of structural compositions. An image processing device is provided with: a means, in an electron microscope having an imaging device and a tilting device that tilts an object to be observed, for tilting said object to be observed in an angle step, and storing the obtained tiled image; a means for aligning the position of said tilted images; a means for generating an initial reconstructed image based on said tilted images; a means for projecting said initial reconstructed image at arbitrarily-defined angles and generating a plurality of projected images; a means for calculating errors in the corresponding pixels between the tilted images and the projection images; a means for determining a processing priority from said errors; a means for calculating the density for each gradation level; a means for determining the processing priority from said densities; and a means for changing the density value of each pixel in the initial reconstructed image in each of the above-mentioned priorities.

The invention claimed is: 
     
       1. A method for processing images using an observation device including: an irradiation device for irradiating an object to be observed with electron beams or X-rays; a detector for detecting responses of the object occurring as a result of irradiation thereof; a holder unit for holding the object; a tilting device capable of arbitrarily setting a tilt angle of the object, comprising the following steps of:
 tilting the object at predetermined angle steps; 
 storing the images which are obtained as 1st to Nth image data observed at respective tilt angles; 
 performing alignment calculation to align the stored 1st to Nth image data; 
 generating an initial reconstructed image from a projection image of the object; 
 projecting the reconstructed image at predetermined angles to generate and store 1st′ to Nth′ image data; 
 performing error calculation to calculate errors in corresponding pixels between the 1st to Nth images and the 1st′ to Nth′ images; 
 determining a processing priority order on the basis of the errors; 
 performing density calculation to calculate a density of pixels for each gradation level; 
 determining a processing priority order on the basis of the densities; and 
 changing a gray level of each pixel in the reconstructed image in each of the processing priority orders. 
 
     
     
       2. The method for processing images according to  claim 1 , wherein each of the gray levels of the image is an integrated value of unit gray levels. 
     
     
       3. The method for processing images according to  claim 1 , wherein a total value of the unit gray levels is the same in all the projection images. 
     
     
       4. The method for processing images according to  claim 1 , wherein a constraint is placed on the initial reconstructed image such that the total value of unit gray levels in a direction parallel to a projection direction for generating the image is invariable. 
     
     
       5. The method for processing images according to  claim 1 , wherein a constraint is placed such that each component of any structure forms a continuum. 
     
     
       6. The method for processing images according to  claim 5 , wherein whether the structure forms the continuum or not is judged on the basis of the density of pixels having a gray level identical to or greater than a predetermined gray level. 
     
     
       7. A method for processing images to define a section of a result obtained by the method for processing images according to  claim 1  for each gray level or any range of gray levels. 
     
     
       8. A method for processing images using an observation device including: an irradiation device for irradiating an object to be observed with electron beams or X-rays; a detector for detecting responses of the object occurring as a result of irradiation thereof; a holder unit for holding the object; and a moving device capable of arbitrarily setting a position of the irradiation device around the object, comprising the following steps of:
 moving the irradiation device at predetermined angle steps; 
 storing images which are obtained as 1st to Nth image data observed at respective movement angles; 
 performing alignment calculation to align the stored 1st to Nth image data; 
 generating an initial reconstructed image from a projection image of the object; 
 projecting the reconstructed image at predetermined angles to generate and store 1st′ to Nth′ image data; 
 performing error calculation to calculate errors in corresponding pixels between the 1st to Nth images and the 1st′ to Nth′ images; 
 determining a processing priority order on the basis of the errors; 
 performing density calculation to calculate a density of pixels for each gradation level; 
 determining a processing priority order on the basis of the densities; and 
 changing a gray level of each pixel in the reconstructed image in each of the processing priority orders. 
 
     
     
       9. The method for processing images according to  claim 8 , wherein each of the gray levels of the image is an integrated value of unit gray levels. 
     
     
       10. The method for processing images according to  claim 8 , wherein a total value of the unit gray levels is the same in all the projection images. 
     
     
       11. The method for processing images according to  claim 8 , wherein a constraint is placed on the initial reconstructed image such that the total value of unit gray levels in a direction parallel to a projection direction for generating the image is invariable. 
     
     
       12. The method for processing images according to  claim 8 , wherein a constraint is placed such that each component of any structure forms a continuum. 
     
     
       13. The method for processing images according to  claim 12 , wherein whether the structure forms a continuum or not is judged on the basis of the density of pixels having a gray level identical to or greater than a predetermined gray level. 
     
     
       14. A method for processing images to define a section of a result obtained by the method for processing images according to  claim 8  for each gray level or any range of gray levels. 
     
     
       15. An X-ray computed tomography system using an observation device including: an irradiation device for irradiating an object to be observed with electron beams or X-rays; a detector for detecting responses of the object occurring as a result of irradiation thereof; a holder unit for holding the object; and a moving device capable of arbitrarily setting a position of the irradiation device around the object, the system further comprising:
 a moving section configured to move the irradiation device at predetermined angle steps; 
 a storage section configured to store images which are obtained as 1st to Nth image data observed at respective movement angles; 
 a calculation section configured to perform alignment calculation to align the stored 1st to Nth image data; 
 an image generating section configured to generate an initial reconstructed image from a projection image of the object; 
 a projecting section configured to project the reconstructed image at predetermined angles to generate and store 1st′ to Nth′ image data; 
 an error calculating section configured to perform error calculation to calculate errors in corresponding pixels between the 1st to Nth images and the 1st′ to Nth′ images; 
 a determination section configured to determine a processing priority order on the basis of the errors; 
 a calculation section configured to perform density calculation to calculate a density of pixels for each gradation level; 
 a determination section configure to determine a processing priority order on the basis of the densities; and 
 a gray level changing section configured to change the gray level of each pixel in the reconstructed image in each of the processing priority orders. 
 
     
     
       16. An image processing system using an observation device including: an irradiation device for irradiating an object to be observed with electron beams or X-rays; a detector for detecting responses of the object occurring as a result of irradiation thereof; a holder for holding the object; and a tilting device capable of arbitrarily setting a tilt angle of the object, the system further comprising:
 a tilting section configured to tilt the observation device at predetermined angle steps; 
 a storage section configured to store the images which are obtained as 1st to Nth image data at respective tilt angles; 
 a calculation section configured to perform alignment calculation to align the stored 1st to Nth image data; 
 an image generating section configured to generate an initial reconstructed image from a projection image of the object; 
 a projecting section configured to project the reconstructed image at predetermined angles to generate and store 1st′ to Nth′ image data; 
 an error calculating section configured to perform error calculation to calculate errors in corresponding pixels between the 1st to Nth images and the 1st′ to Nth′ images; 
 a determination section configured to determine a processing priority order on the basis of the errors; 
 a calculation section configured to perform density calculation to calculate a density of pixels for each gradation level; 
 a determination section configure to determine a processing priority order on the basis of the densities; and 
 a gray level changing section configured to change the gray level of each pixel in the reconstructed image in each of the processing priority orders. 
 
     
     
       17. The image processing system according to  claim 16 , wherein the number of iterations of the error calculation and the number of iterations of the density calculation can be set individually. 
     
     
       18. An image processing system using an observation device including: an irradiation device for irradiating an object to be observed with electron beams or X-rays; a detector for detecting responses of the object occurring as a result of irradiation thereof; a holder unit for holding the object; and a moving device capable of arbitrarily setting a position of the irradiation device around the object, the system further comprising:
 a moving section configured to move the irradiation device at predetermined angle steps; 
 a storage section configured to store images which are obtained as 1st to Nth image data observed at respective movement angles; 
 a calculation section configured to perform alignment calculation to align the stored 1st to Nth image data; 
 an image generating section configured to generate an initial reconstructed image from a projection image of the object; 
 a projecting section configured to project the reconstructed image at predetermined angles to generate and store 1st′ to Nth′ image data; 
 an error calculating section configured to perform error calculation to calculate errors in corresponding pixels between the 1st to Nth images and the 1st′ to Nth′ images; 
 a determination section configured to determine a processing priority order on the basis of the errors; 
 a calculation section configured to perform density calculation to calculate a density of pixels for each gradation level; 
 a determination section configure to determine a processing priority order on the basis of the densities; and 
 a gray level changing section configured to change the gray level of each pixel in the reconstructed image in each of the processing priority orders. 
 
     
     
       19. The image processing system according to  claim 18 , wherein the number of iterations of the error calculation and the number of iterations of the density calculation can be set individually. 
     
     
       20. The image processing system according to  claim 18 , further comprising:
 an image/gradation level changing section configured to change the image data to gradation-level representations; 
 a gradation composition/image changing section configured to change each composition of the gradation-level representations to image data using a plurality of images; and 
 a gradation/image changing section configured to change the gradation-level representations to image data. 
 
     
     
       21. The image processing system according to  claim 20 , wherein each composition of the gradation-level representations is changed using a plurality of images such that it forms a continuum. 
     
     
       22. The image processing system according to  claim 21 , wherein whether each composition of the gradation-level representations forms a continuum or not is judged on the basis of the density of each composition of the gradation-level representations.